Metallic lens antennas



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METALLIC LENS ANTENNAS Original Filed Sept. 9, 1947 3 Sheets-Sheet 2 1N VEN TOR5 A/aa M. 057W@ BY daf/,v E #Msgr ffm ifm/wif Sept. 25, 1956 N. M. RUST ET AL 2,764,757

METALLIC LENS ANTENNAS Original Filed Sept. 9, 1947 3 Sheets-Sheet 3 United States Patent NETALLIC LENS ANTENNAS Noel Meyer Rust and .lohn Forrest Ramsay, Chelmsford, England, assignors, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware (lriginal application September 9, 1947, Serial No. 772,960, now Patent No. 2,650,935, dated September 1, 1953. Divided and this application January 2, 1951, Serial No. 214,450. ln Great Britain March 19, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires March 19, 1966 16 Claims. (Cl. 34E- 783) This invention relates to radio horns, that is to say horn-like devices for directing very high frequency radio energy. Radio horns have a considerable field of application e. g. to communication systems, navigation aiding systems (especially for aircraft use) and radar systems. This application is a division of U. S. application Serial No. 772,969, filed September 9, 1947, issued on September l, 1953, as Patent No. 2,650,985.

One of the difficulties encountered in the use of horns whether fed by wave guides or other means is that the lengths of the paths from the small end or virtual apex of the horn to different points in the plane of its aperture are different with the result that the field is not uniform in phase over the said plane and, in general, uniformity or" phase of field over the aperture is necessary to etilcient radiation. In the case of a horn of wide aperture in relation to the wave length, and of length comparable to the aperture, this defect becomes serious, being very detrimental to the directivity of the horn, and imposes serious constructional limitations since if a good standard of directivity is to be maintained the horn must be made of great length which results either in excessive bulk or expensive and complicated folding. The present invention seeks to reduce or avoid this defect and the limitations resulting therefrom.

The invention is based upon the fact that the phase of field in a space bounded on at least two sides by conductive walls placed parallel to the electric field and not less than half a wave length apart progresses at a velocity greater than the velocity in free space, this increase in velocity resulting from the interaction of waves reflected from the boundary walls. This lleld velocity or phase velocity may be controlled by controlling the spacing of the boundary walls, this spacing being, of course, always not less than a half wave length.

The present invention is based upon the above mentioned physical phenomenon and consists in its main feature in utilising the said phenomenon to compensate for the effect of different path lengths between apex and aperture of a horn so as to ensure that despite different path lengths there is a pre-determined phase distribution which is usually required to be uniformity of phase over the said aperture. The simplest and most common case is that in which the aperture lies in a geometrical, i. e. a flat plane, but the invention is not limited to this case and may be employed in cases in which the aperture lies on a curved surface e. g. a cylindrical surface. Again the aperture need not actually be across the mouth of a horn proper; as will be seen later it may be across the mouth of an attachment to a horn, the attachment being then regardable as part of a horn structure consisting of the horn proper and the attachment.

According to the main feature of this invention a radio horn structure comprises means for differently modifying the velocity of propagation over different paths from 2,764,757 Patented Sept. 25, 1956 apex to aperture so as to compensate or correct to a desired degree for the effects of the different lengths of said paths on phase distribution across said aperture.

The invention is illustrated in and further explained in connection with the accompanying drawings.

There are various methods by which the invention may be carried into effect and these methods may be used either singly or in conjunction.

One method is to provide horn partition plates of predetermined shape, extent and disposition which in effect divide up the horn into wave guide sections so dimensioned as to produce increase of velocity (as compared to the velocity in free space) so as to compensate for different path lengths in the horn and give uniformity of phase across the aperture.

Another method is to provide a horn with an attachment whose inner space is subdivided by suitably shaped and disposed plates into what are in effect wave guides which produce velocity changes such that uniformity of phase is obtained at the aperture of the attachment.

A third method consists in constricting the horn by giving it what may be termed delayed flaring up or advanced flaring down, that is to say, flaring up or down so as to produce required velocity changes to compensate for different path lengths.

The invention will be described in greater detail by reference to the following description taken in connection with the accompanying drawing wherein similar reference letters refer to similar elements and in which:

Figures l and 2 are cross-sectional and end views respectively of an embodiment of the invention including a wave guide horn flared in one dimension only;

Figure 3 is a cross-sectional view of an embodiment of the invention wherein the horn is flared in two dimensions;

Figure 4 is a partially cut-away, perspective view of the embodiment of Figure 3;

Figure 5 is a partially cut-away, perspective view of an embodiment of the invention including a horn extension with a bi-concave electromagnetic lens positioned therein;

Figures 6-9 are cross-sectional views of various electromagnetic lens arrangements according to the invention;

Figure 10 is a partially cut-away, perspective view of an alternative embodiment of the invention similar to the one shown in Figure 4;

Figure 11 is a partially cut-away, perspective view of an embodiment of the invention employing steppedback lens plates;

Figure 12 and 12a are perspective and plan views. respectively, of an electromagnetic lens mounted in the extension of a folded horn;

Figures 13 and 14 are respective cross-sectional and end views of an electromagnetic lens positioned in a skew horn;

Figures l5 and 16 are respective cross-sectional and end views of an electromagnetic lens positioned in a skew horn; the lens and horn are of different ty es than the ones shown in Figures 13 and 14; and

Figure 17 is a perspective view of a bicone antenna arrangement including an electromagnetic lens according to the invention.

Referring to Figures 1 and 2 which show in diagrammatic section and end view respectively one embodiment of the invention as applied to a horn flared out in one plane only for use with waves with polarisation perpendicular to the plane of flaring, the horn is divided into what are in eect a series of wave guide sections GS by means of plates P at right-angles to the parallel wal: of the horn the plates being radial as viewed in a direction perpendicular to said parallel walls (re as viewed in Figure 1) so that the plates all point from the mouth of the horn towards the apex. The plates nearest the ared walls are longest and diminish in length towards the centre of the horn so that the velocity increase in the outermost wave guide sections is greater than that in the more inward sections whereby the greater lengths of the outer paths from apex to aperture are compensated. Typical practical dimensions in terms of the wave length 2 are indicated in Figure l.

The principle embodied in the construction just described may be extended as shown in Figures 3 and 4 to a horn which is ared in both planes. Figure 3 is a diagrammatic axial section and Figure 4 a perspective view. As will be seen the sub-dividing plates are not only of varied length but their inner edges are curved (see Figure 4) whereas in the case of Figures l and 2 for a horn flared in one plane only the ends of the subdividing plates may be simply straight.

In another class of embodiment, instead of providing path length correcting velocity increasing plates in the ared part of the horn, a straight rectangular horn extension may be provided and suitably shaped and disposed sub-dividing plates mounted across the extension so that although there will not be uniformity of phase Where the energy enters the extension there will be the desired uniformity across what is now the effective aperture of the whole horn structure (comprising horn proper and extension) i. e. where the energy leaves the extension. Plates sub-dividing such an extension into wave guide sections may be simple rectangular plates of different sizes or they may be plates with inner curved edges. Figure 5 is an embodiment of this nature, the horn proper being indicated at H and the extension at X, the plates curved on both edges, being shown at P. Figure ll illustrates an alternative embodiment, this one employing stepped-back double concave electromagnetic lens plates. The particular arrangement in any case will depend upon design requirements and the plates will be horizontally or vertically disposed in dependence upon the plane of polarisation.

For all embodiments in accordance with this invention the partition plates may be of uniform spacing with their lengths varied or they may be or' uniform length with their spacing varied or both spacing and length may be varied to provide the required compensation. These three possibilities are indicated in Figures 6 to 8, Figure 6 showing constant spacing and varied length, Figure 7 showing varied spacing and constant length and Figure 8 showing both length and spacing varied. Again the spacing of the plates may, if desired, be varied over the individual lengths of the wave guide sections formed thereby. Where both length and spacing are varied the design may be and preferably is such that each wave guide section is an integral number or" half wave lengths long, i. e. an integral number of half wave lengths in the wave guide. This design expedient has the advantage of facilitating matching the impedance of the horn to the impedance of a feeding wave guide.

The methods of carrying out the invention which consist in providing partition walls in a horn or in an extension to the horn may be employed in combination. For example, a horn structure may comprise as shown in Figure 9 a horn proper H and a parallel sided box like extension X with partition plates P shaped and dimensioned to produce the required compensation for different path lengths arranged in the extension member and also extending into the horn proper. In the case shown the partition plates P are angularly bent where they pass from the horn proper H into the extension X, parts of the plates lying parallel to the extension axis and parts lying parallel to the flared sides of the horn proper as shown. The plates P may be bent over as indicated and by suitable adjusting the angles of bending of the individual plates a degree of control of the amplitudes of the energies entering the individual wave guide sections GS and a degree of control of the amplitude distribution across the horn thereby obtained. This is indicated in Fig. 9 by showing alternative angles of bending for two of the plates in broken lines.

Where it is desired to produce a horn of wide aperture in the E plane (electric plane) but narrow aperture in the H plane (magnetic plane) the opposite to delayed flaring may be used, i. e. the narrowing down from feeder wave guide dimension to the required narrow aperture dimension may be carried out earlier for the outer paths than for the inner and central paths, the design being again such as to produce a substantially equi-phase aperture. In order to avoid defects due to the ray paths being bent by refraction it is desirable, and in some cases may be found essential, to provide suitably disposed metal plates normal to the direction or" the electric eld at the entrance to the phase correcting part of the horn and extending along this part in such a way as to guide the wave elements. These plates should not be confused with those which divide a horn with wave guide sections, rior the latter are parallel to the electric eld and therefore at right angles to the former. Again such metal plates which extend normal to the electric eld and to the extension of the velocity modifying plates and which may be termed bafiles may be provided in other constructions in accordance with this invention, e. g. in a horn extension, the baiiies, in conjunction with the velocity modifying plates then resulting in a honeycomb like or cellular structure. An arrangement of this type is shown at BP in Figure l0. It is understood that any other of the arrangements may likewise be provided with baie plates.

The expedients of velocity modication by delayed liaring up or flaring down; by constriction; and by partition plates sub-dividing the horn plates into wave guide sections may be adopted in any desired combination each of the expedients adopted contributing its quota to the total velocity modication introduced. Further the methods of the invention are not limited to their application to straight horns for obviously they may be employed also for folded horns. Figures 12 and 12a show a folded horn with an extension X housing plates P. They are also very advantageous when applied to the construction of what may be termed skew horns or part horns. This is a very important class of embodiment practically. In one embodiment of this class illustrated in the mutually perpendicular views of Figures 13 and 14 a skew horn or part horn H is, in effect, a normally shaped horn which is cut away along a plane parallel to the axis-for example along a plane passing through the axis-and mounted on a flat surface (e. g. the ground G) with the plane of cutting on that surface. Thus where the cutting plane passes through the axis the result would be a half-horn resting on the flat surface.

By means of partition plates P and/or flaring provided in `accordance with this invention the phase distribution across the mouth of the half horn may be made such as to give a directional beam parallel to the axis although the horn is not geometrically symmetrical with respect to the axis. The plates P may be bent over and, as in Fig. 9 a degree of control of the amplitude distribution across the horn obtained by suitably adjusting the angles of bending (indicated in broken line for one plate). Figures 15 and 16 show another construction of this type for the case where the electric iield is at right-angles to that for Figures 13 and 14. In Figures 13 and 15 the direction of the electric field is indicated conventionally at E. The great practical advantage of this type of construction is that the energy feeding apparatus at the small end of the horn may be brought at or near ground or building level--an advantage leading to great constructional convenience and economy.

The principles of the invention may be extended to socalled bi-cones which produce circular polar diagrams, in all horizontal planes and a relatively sharp beam in all vertical planes. For example in the case of a bi-cone exciting vertically polarised waves phase correction may be effected by vertical partition plates of suitable varying profile arranged radially round the periphery of the bi-cone structure. In the case of a bi-cone excited by bent dipoles or by loops to produce an all-round horizontally polarised iield, phase correction may be effected in accordance with this feature of the invention by providing a plurality of parallel peripheral ring plates round the bicone structure and of different radial lengths, those nearest the centre being shorter than the outer ones. In the case of bi-cones with very large cylindrical apertures it is very convenient to omit the outer parts of the bi-cone. In such a case a suitable construction of partition plates may be provided at a little distance from the actual bi-cone orifice. One form of bi-cone structure in accordance with the invention is illustrated, in Figure 17 in which the bicone BC with energy radiating slots at S is provided with ring plates P.

In all cases in accordance with this invention in which the path differences to be corrected for exceed a wave length, that is to say in which the lengths of the paths for which correction is to be applied exceed the shortest path by one or more wave-lengths, it is necessary only to correct for such path differences in excess of a wave length as an integral number of wave lengths will clearly not introduce any phase change. In other words partition plates or other devices provided in carrying out this invention may be of stepped construction being stepped back at each point or points corresponding to a path difference of an integral number of wavelengths as shown in Fig. ll. Further although the partition plates and other conducting surfaces have been specifically described as plates or surfaces of solid material it will be obvious to those skilled in the art that they may be perforated for lightness or to reduce windage or made of wires or gauze (as may be desired) for the same reasons and the term plates is intended to cover all such constructions.

Although the invention has been described with reference to the transmission of radio energy it will be apparent to those skilled in the art that the constructions described herein may also be used for reception if desired since a radio horn is in essence a reversible device.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

1. A radio antenna system comprising a wave guide having an apex at one end thereof adapted to be connected to a radio frequency transducer means and an aperture at the other end thereof open to free space and partition plates arranged within said wave guide to divide said wave guide into a number of wave guide sections, each an integral number of half waves long in the direction of energy propagation, at the operating frequency, to provide a desired phase distribution relationship between said apex and said aperture.

2. A radio antenna system comprising a wave guide having an apex at one end thereof adapted to be connected to a radio frequency transducer means and an aperture at the other end thereof open to free space and partition plates arranged Within said wave guide to divide said waveguide into a number of waveguide sections, each an integral number of half wavelengths long in the direction of energy propagation, at the operating frequency, to provide a desired phase distribution relationship between said apex and said aperture, said Wave guide being in the shape of a horn.

3. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of spaced-apart, parallel, dat, conductive plates arranged adjacent one another in a direction perpendicular to said axis with width dimensions parallel to each other and to said axis, said width dimensions successively decreasing from the outer portion of said lens to the center portion of said lens, and said plates being spaced closer to one another at the outer portion of said lens than at the center portion of said lens.

4. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of spaced-apart, flat, rectangular, conductive plates arranged in a direction perpendicular to said axis with said at surfaces adjacent one another, said plates being of successively greater widths in the direction toward the outer portion of said lens, whereby at least one set of longitudinal edges of said plates define a generally concave contour surface.

5. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of spaced-apart, parallel, flat, rectangular, conductive plates arranged adjacent one another in planes parallel to said axis, said plates being of successively smaller widths from the outer to the center portions of said lens and being spaced apart successively smaller amounts from the center of said lens to the outer portion of said lens.

6. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of spaced-apart, llat, rectangular, conductive plates arranged adjacent one another in a direction perpendicular to said axis and with respective width dimensions lying in planes converging toward said focus, said plates being of successively increasing widths from the center of said lens to the outer portion of said lens.

7. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of spaced-apart, at, conductive plates arranged adjacent one another in a direction perpendicular to said axis, said plates including first portions of rectangular shape having width dimensions parallel to each other and to said axis, said width dimensions successively increasing in magnitude in the direction of the outer portion of said lens, and said plates including second portions closer to said focus than said first portions and converging toward said focus.

8. An electromagnetic lens as set forth in claim 7, wherein said second portions of said conductive plates are of rectangular shape.

9. An electromagnetic lens as Set forth in claim 8, wherein said second portions have width dimensions of successively increasing size in the direction of the outer portion of said lens.

l0. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of adjacent dielectric channels extending in a direction per pendicular to said axis, each channel comprising a pair of flat, rectangular, metallic members and a dielectric medi um included therebetween, said members having one set of longitudinal edges facing toward said focus and constituting a generally concave side of said lens, said channels being of successively increasing lengths from the Center to the outer portion of said lens.

1l. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of adjacent dielectric channels lying in a direction perpendicular to said axis, each channel comprising a pair of flat, metallic members and a dielectric medium included therebetween, said members having one set of longitudinal edges facing toward said focus and constituting a generally concave side of said lens, and another set of longitudinal edges facing away from said focus and constituting a generally at contour surface, successive ones of said channels being of successively increasing lengths from the center of said lens to the outer portion of said lens and the widths of said channels in said direction perpendicular to said axis being less at the outer portion of said lens than at the center portion of said lens.

12. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of adjacent dielectric channels lying along a line perpendicular to said axis, each channel comprising a pair of flat, rectangular, metallic members and a dielectric medium included therebetween, said members all lying in radial planes converging toward said focus and being formed with one set of longitudinal edges facing toward said focus and constituting a generally concave side of said lens, and another set of longitudinal edges facing away from said surface and defining a generally plane contour surface.

13. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of adjacent dielectric channels lying along a line perpendicular to said axis, each channel comprising a pair of rectangular metallic members and a dielectric medium included therebetween, said rectangular members being formed of two portions, one having surfaces parallel to each other and to said axis and the other having surfaces lying in planes converging toward said focus, said other portions being closer to said focus than said one portions, said other portions being formed with a set of longitudinal edges facing toward said focus and constituting a generally concave side of said lens.

14. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of adjacent dielectric channels lying along a line perpendicular to said axis, each channel comprising a pair of rectangular, metallic members and a dielectric medium included therebetween, said rectangular members being formed of two portions, one having surfaces parallel to each other and to said axis and the other having surfaces lying in planes converging toward said focus, said other portions being closer to said focus than said one portions, said other portions being formed with a set of longitudinal edges facing toward said focus and constituting a generally concave side of said lens, and said one portions being formed with a set of longitudinal edges facing away from said focus and constituting a gener-ally dat side of said lens.

15. An electromagnetic lens having a focus and an axis passing through said focus comprising a plurality of adjacent dielectric channels lying along a line perpendicular Y to said axis, each channel comprising a pair of rectangular,

metallic members and a dielectric medium included therebetween, said rectangular members being formed of two portions, one having surfaces parallel to each other and to said axis and the other having surfaces lying in planes converging toward said focus, said other portions being closer to said focus than said one portions, said other portions being formed with a set of longitudinal edges facing toward said focus and constituting a generally concave side of said lens, and said one portions being formed with a set of longitudinal edges facing away from said focus and constituting a curved generally concave contour surface.

16. A radio antenna system as set forth in claim 2, wherein said horn comprises a skew horn.

References Cited in the le of this patent UNITED STATES PATENTS 2,206,683 Wolif July 2, 1940 2,283,935 King May 26, 1942 2,401,601 Atwood July 4, 1946 2,405,242 Southworth Aug. 6, 1946 2,411,872 Feldman et al. Dec. 3, 1946 2,415,807 Barrow et al Feb. 18, 1947 2,442,951 Iams June 8, 1948 2,461,005 Southworth Feb. 8, 1949 2,562,277 Kock July 31, 1951 2,591,695 Hansen Apr. 8, 1952 OTHER REFERENCES Electronics, March 1, 1946, page 100. Kock-Metal Lens Antenna BSTJ Technical publication, published in Proceedings IRE, November 1946. 

